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JavaScript RegExp Object

Posted by  Danish Khan
on    October-19-2012 15:13 PM

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JavaScript RegExp Object

Introduction:

In this article I am going to explain you about the RegExp Object it is a short form of Regular Expression. Which are very important because they provide us pattern-matching, search and replacing of text possible in JavaScript?

Syntax:

    var pat=new RegExp(pattern,attributes);

    or more simply like

    var pat=/pattern/modifiers;

 

In the above syntax pattern specifies the expression which we are going to search for

And the attributes specify that if a search is going to be global or case-sensitive etc.

Brackets:

Brackets have a special meaning when used with Regular Expression they are used basically to specify range of characters.

Expression

Description

 

[. . .]

Find any character between the bracket.

[^. . .]

Find any character not between the bracket.

[0 - 9]

It matches any decimal digits from 0-9.

[a – z]

It matches any character from lowercase letter a to lowercase letter z.

[A – Z]

It matches any character from uppercase letter A to uppercase letter Z.

[a –Z]

It matches any character from lowercase letter a to uppercase letter Z.

 

 

 

The above ranges shown are general we can create our own like [0-6] it will match any decimal between 0 and 6 likewise we can match any characters [a-d], matches all the characters between character a to z.

Metacharacters:

Metacharacters are simply alphabetical characters which have special meaning; they are proceeding with a backslash which give a special meaning to the combination.

Expression

Description

 

.

It is used to find a single character except newline or line terminator.

\w

It is used to find word character (a-z,A-Z,0-9 and Underscore).

\W

It is used to find a non-word character.

\d

It is used to find a digit from 0-9.

\D

It is used to find all non-digit character.

\s

It is used to find white space character (space,tab,newline)

\S

It is used to find non-whitespace character.

\b

It is used to find a match at the beginning of a word.

\B

It is used to find a match not at the beginning or end of a word.

\0

It is used to find a NULL character.

\n

It is used to find a newline character.

\r

It is used to find a tab character.

Quantifiers:

The frequency of bracketed characters and single characters can be denoted by a special character, each of the special character have some specific meaning.

Quantifiers

Description

 

p+

It will match any string which contains minimum one p or more.

p*

It will match any string that contains zero or more occurrences of p.

p?

It will match any string that contains zero or one occurrences of p.

p{N}

It will match any string that contains a sequence of N p’s.

p{x,y}

It will match any string that contains the sequence of x to y p’s.

p{x}

It matches any string that contains a sequence of at least x p’s.

p$

It matches any string with p at the end of it.

^p

It matches any string which is started at p.

 

 

Example showing the use of RegExp:

 

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title>Regexp Example in JavaScript</title>

    <script type="text/javascript">

        function regExpress() {

            var str = "This is a first example of RegEx";

            var pattern1 = /example/;

            document.write(str.match(pattern1));

        }

    </script>

</head>

<body onload="regExpress()">

</body>

</html>

 

Output:

JavaScript RegExp Object

 

 

RegExp Methods:

Method

Description

exec()

It is used to execute a search for a string parameter passed to it. If no match found returns null.

Test()

It searches string for text that matches regExp. It returns true or false.

toString()

It returns the string representation of a specified object.

toSource()

It returns the object literal of the specified object and we can use this to create a

new object

 

Example of test method in RegExp:

 

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title>Regexp Example in JavaScript</title>

    <script type="text/javascript">

        function regExpress() {

            var pattern1 = new RegExp("example");

            document.write(pattern1.test("This is a example of test method"));

        }

    </script>

</head>

<body onload="regExpress()">

 

</body>

</html>

 

Output:

true

 

Example of exec method in RegExp:

 

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title>Regexp Example in JavaScript</title>

    <script type="text/javascript">

        function regExpress() {

            var pattern1 = new RegExp("example");

            document.write(pattern1.exec("This is a example of test method"));

        }

    </script>

</head>

<body onload="regExpress()">

</body>

</html>

 

Output:

Example

 

 

Perform case-insensitive matching:

 

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title>Regexp Example in JavaScript</title>

    <script type="text/javascript">

        function regExpress() {

            var str = "This is a first Example of RegEx";

            var pattern1 = /example/i;

            document.write(str.match(pattern1));

        }

    </script>

</head>

<body onload="regExpress()">

</body>

</html>

 

Output:

Example

 

Display all matches with the characters specified in the brackets:

 

 

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title>Regexp Example in JavaScript</title>

    <script type="text/javascript">

        function regExpress() {

            var str = "This is a first Example of RegEx";

            var pattern1 = /[a-f]/ig;

            document.write(str.match(pattern1));

        }

    </script>

</head>

<body onload="regExpress()">

</body>

</html>

 

Output:

JavaScript RegExp Object

 

 

 

Example showing the use of Metacharacters

 

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title>Regexp Example in JavaScript</title>

    <script type="text/javascript">

        function regExpress() {

            var str = "This is a first example of RegEx";

            var pattern1 = /ex.mple/;

            document.write("Metachar example: " + str.match(pattern1));

        }

    </script>

</head>

<body onload="regExpress()">

</body>

</html>

 

Output:

JavaScript RegExp Object

 

Example to find a word in a given string:

 

 

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title>Regexp Example in JavaScript</title>

    <script type="text/javascript">

        function regExpress() {

            var str = "This is a first example of RegEx";

            var pattern1 = /\w/g;

            document.write("Metachar example: " + str.match(pattern1));

        }

    </script>

</head>

<body onload="regExpress()">

</body>

</html>

 

Output:

JavaScript RegExp Object

 

 

This example will search for the non-word character:

 

 

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title>Regexp Example in JavaScript</title>

    <script type="text/javascript">

        function regExpress() {

            var str = "ab *&^ cd @! ef";

            var pattern1 = /\W/g;

            document.write("Metachar example: " + str.match(pattern1));

        }

    </script>

</head>

<body onload="regExpress()">

</body>

</html>

 

Output:

JavaScript RegExp Object

 

 

 

This example is used to search for digits:

 

 

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title>Regexp Example in JavaScript</title>

    <script type="text/javascript">

        function regExpress() {

            var str = "ab123cd456ef";

            var pattern1 = /\d/g;

            document.write("Metachar example: " + str.match(pattern1));

        }   

    </script>

</head>

<body onload="regExpress()">

</body>

</html>

 

Output:

JavaScript RegExp Object

 

 

 

This example is to find out the non-digit characters:

 

 

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title>Regexp Example in JavaScript</title>

    <script type="text/javascript">

        function regExpress() {

            var str = "ab453!*fg45)(";

            var pattern1 = /\D/g;

            document.write("Metachar example: " + str.match(pattern1));

        }

    </script>

</head>

<body onload="regExpress()">

</body>

</html>

 

Output:

JavaScript RegExp Object

 

 

This example is to find out the white-space character :

 

 

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title>Regexp Example in JavaScript</title>

    <script type="text/javascript">

        function regExpress() {

            var str = "This is example to find whitespace character";

            var pattern1 = /\s/g;

            document.write("Metachar example: " + str.match(pattern1));

        }

    </script>

</head>

<body onload="regExpress()">

</body>

</html>

 

Output:

JavaScript RegExp Object

 

 

This example is about the use of b metachar to find a match at the beginning of a word:

 

 

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

    <title>Regexp Example in JavaScript</title>

    <script type="text/javascript">

        function regExpress() {

            var str = "This is example to find whitespace character";

            var pattern1 = /\bex/g;

            document.write("Metachar example: " + str.match(pattern1));

        }

    </script>

</head>

<body onload="regExpress()">

</body>

</html>

 

 

 

Conclusion:

In this article I gave introduction to RegExp and what are the various uses in JavaScript through various examples.
















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